Delusional disorder

Symptoms and key features

• one or more delusions, meaning fixed beliefs that stay put in the face of clear evidence against them
• present for at least a month
• day-to-day functioning that's mostly intact outside the area the belief touches
• no prominent hallucinations, disorganized speech, or other features of schizophrenia
• behavior that isn't obviously bizarre or odd, apart from actions driven by the belief
• little or no recognition that the belief might be wrong

What it looks like

The beliefs are often about things that could happen in real life. That's what makes them hard to spot. The MSD Manual and DSM-5-TR describe several recognized subtypes:

• Persecutory: being followed, spied on, cheated, poisoned, or harassed. People may file complaint after complaint or lawsuit after lawsuit.
• Jealous: certainty that a partner is unfaithful, built on tiny clues like a phone left face down or a car parked differently.
• Erotomanic: a belief that another person, often someone of higher status, is secretly in love with them.
• Somatic: a conviction about the body, like an infestation, a foul smell no one else notices, or a part that's misshapen.
• Grandiose: a belief in a great, unrecognized talent, discovery, or special relationship.

Picture a retired accountant who's sure his upstairs neighbors pump gas through the vents to drive him out. He's sealed the vents, bought three air monitors that read normal, and moved his bed twice. He's polite, organized, and articulate. His daughter notices he's stopped inviting anyone over and has written eleven letters to the building manager.

What people often confuse this with

Schizophrenia. Schizophrenia usually brings hallucinations, disorganized thinking, and a broad decline in function. In delusional disorder, the belief tends to stand alone and daily life often holds together.

Paranoid personality disorder. Paranoid personality disorder is a lifelong style of suspicion and distrust. It doesn't reach the fixed, specific certainty of a delusion.

A strongly held opinion or a group belief. Beliefs shared by a person's culture or religion aren't delusions. Clinicians have to take culture into account, and that takes time and care.

OCD or body dysmorphic disorder. People with body dysmorphic disorder can be absolutely convinced they look deformed. When insight is fully absent, DSM-5-TR asks clinicians to keep the BDD diagnosis and note the absent insight, rather than switch to delusional disorder.

Delirium or dementia. New delusions in an older adult, especially with confusion, need a medical workup first. See delirium.

What research says

• The trial evidence is sparse. A 2015 Cochrane review found only one randomized trial it could include, with 17 people completing CBT versus supportive therapy. It couldn't use any medication trials because the data were poorly reported. The authors concluded that high quality trials are badly needed.
• Clinical experience supports antipsychotics. Most guidance on medication comes from case series and clinical practice, not controlled trials. That's worth knowing when you're weighing options with a psychiatrist.
• Course varies. The MSD Manual notes that delusional disorder doesn't usually cause severe impairment or personality change, though the concerns can slowly grow, and that most people can keep working as long as the job doesn't touch the subject of the belief.

How it's diagnosed

A clinician diagnoses delusional disorder through a careful interview, often over more than one visit, plus information from family where the person agrees. Under DSM-5-TR, the core criteria are one or more delusions lasting at least a month, never meeting criteria for schizophrenia, function that isn't markedly impaired beyond the delusion's reach, and mood episodes that are brief compared with the delusional periods.

Ruling out other causes matters, because delusions can come from many places:

• medical and neurological conditions, including dementia, delirium, brain injury, and thyroid disease
• substances, especially stimulants like amphetamines and cocaine
• other psychiatric conditions, including schizophrenia, mood disorders with psychotic features, and OCD or body dysmorphic disorder with poor insight

Diagnosis usually includes a physical exam, blood work, a medication and substance review, and sometimes brain imaging, especially when the beliefs start later in life.

Why it happens

Nobody knows yet. The MSD Manual notes it's relatively uncommon compared with schizophrenia and usually starts in middle or later adult life, and that the consequences of the belief, like isolation and conflict at home or work, are often what cause the most harm. Because the condition is uncommon and people with it rarely seek care on their own, it's been hard to study, and there's no solid research on risk factors yet.

Treatment

Building trust comes first. Arguing with a delusion almost never works and usually ends the conversation. Good clinicians neither agree nor debate. They focus on the distress, sleep, relationships, and practical consequences the person does care about, and treatment grows from there.

Medication. Antipsychotics are the most commonly used treatment. Some people improve substantially. Others get partial relief, with the belief losing its grip even if it doesn't disappear. The PsychiatryRx guide to antipsychotics covers how the class works and its side effects.

Psychotherapy. CBT adapted for psychosis aims to loosen certainty gradually and reduce distress, instead of winning an argument. It's promising, but tested in very few people.

Treating what comes with it. Depression or anxiety can come along with delusional disorder, and they deserve treatment in their own right.